1. Filed of the Invention
The present invention relates to a mobile communication system and a method for controlling receiving quality in the mobile communication system. More specifically, the present invention relates to a mobile communication system that provides communication services from a base station to a mobile station via a radio channel and a method for controlling receiving quality in the mobile communication system.
2. Description of the Related Art
In a known mobile communication system, a desired receiving quality is achieved mainly by controlling transmission power to compensate for an instantaneous variation in received signal level.
FIGS. 1A to 1C show problems with receiving quality control using conventional transmission power control. It is assumed that the receiving range varies over a wide range as shown in FIG. 1A. In this case, if the transmission power is controlled by a small step size (see FIG. 1B), transmission power control cannot follow rapid variations in receiving level. On the other hand, if the transmission power is controlled by a large step size (see FIG. 1C), transmission power control cannot accurately follow variations in receiving level.
To solve the conventional problems described with reference to FIGS. 1A to 1C, the transmission power control based on a small step size must be executed at a very short control period. In this case, a new problem occurs; the overhead of a control signal for the transmission power control may reduce transmission efficiency.
In particular, it is known that the level of received signals in a mobile communication system varies very dynamically. To compensate for such received signals, the transmission power must be controlled over a wide dynamic range. Consequently, it is difficult to apply an efficient power amplifier.